1. Field of the Invention
The present invention relates to a coordinator's data transmission method, a device's data reception method, a coordinator using the data transmission method and a device using the data reception method in a Zigbee system, and more particularly to a coordinator's data transmission method using a direct transmission method, a device's data reception method, a coordinator using the coordinator's data transmission method and a device using the device's data reception method in a Zigbee system.
2. Discussion of Related Art
Zigbee is a standard for low-data-rate communications and it is designed for low power so that one battery can last for about a year in a Zigbee system. It costs about a half in comparison with a Bluetooth system by minimizing the number of software and relational compartments. Therefore, it is suitable for a home network operating based on control devices and sensors in a wireless communication technology. Further, the Zigbee standard is advantageous in that it enables several tens of thousands of devices to connect in a network while the Bluetooth can connect at most several hundred devices in a network.
FIG. 1 illustrates a conceptual diagram showing a data transmission/reception method in accordance with a related art. A typical data transmission/reception method will be described below with reference to FIG. 1.
The basic goal of the Zigbee is to facilitate communication between devices 20 minimizing power consumption of each device 20. Accordingly, a coordinator 10 for coordinating a Zigbee system and a plurality of devices 20 always keeps its state as RX_ON and each device 20 normally keeps its state as RX_OFF. In a case where data transmission occurs from the devices 20 to the coordinator 10, direct transmission is possible. But direct transmission is not possible for data transmission from the coordinator 10 to the devices 20.
In a case where the coordinator 10 has data to be transmitted to the devices 20 in a Zigbee system, the data can not be directly transmitted to the corresponding device 20 but the coordinator 10 informs the device 20 of existence of data by a beacon frame. That is, an address of the corresponding device 20 to receive the data is recorded in a pending address field of the beacon frame, and then the beacon frame is transmitted to the corresponding device 20. The corresponding device 20 which received the beacon frame recognizes that there is data to be received from the coordinator 10 and then makes and sends a data request command to the coordinator 10. As described above, after the device 20 sends the data request command, it keeps its state as RX_ON and can then receive the data from the coordinator 10.
That is, even if the coordinator 10 has data to be transmitted to the device 20, the coordinator 10 can not directly transmit the data but indirectly transmits the data after receiving the data request command from the device 20.
In conclusion, the coordinator 10 can transmit data to the device 20 only in an indirect transmission method in a conventional Zigbee system in a case where the coordinator 10 transmits data to the device 20. Accordingly, the conventional Zigbee system is disadvantageous in that it consumes power to exchange a data request command and an acknowledgement ACK thereof between the coordinator 10 and the devices 20. Further, the conventional Zigbee system is disadvantageous in that it wastes power due to message collision between the data request commands and the data, which occurs when the coordinator 10 and a plurality of the devices 20 communicate with each other. Still further, the conventional Zigbee system is disadvantageous in that there occurs a delay time to transmit data to the device 20 because the coordinator 10 can not directly transmit data to the device 20 and must wait until it receives the data request command from the device 20.